Wash the sloes;, Dry on kitchen paper or a tea towel.
Put in kitchen plastic bag and level the sloes, put something flat and heavy on top and roll gently. Put bag and contents into freezer (on Fast Freeze if poissible) to burst the sloes.
Once frozen empty bag into glass container - wide mouthed bottle, large Jam Jar or similar. Add some sugar and cover with gin.
Leave 'til gin takes on deep purple colour, Drain into another bottle.
Add more gin to sloes and repeat exercise - will take longer and flavour won't be as strong.
If you wish - pour some (cheap) sherry over sloes and leave for 4 to 6 weeks, drain liquid into another bottle.
Enjoy !!!